The present invention relates to tubes for passing a refrigerant therethrough, i.e., refrigerant tubes, for heat exchangers, and more particularly to refrigerant tubes for condensers for use in car coolers.
The term "aluminum" as used herein and in the claims includes pure aluminum and aluminum alloys.
Examined Japanese Patent Publication No. 45300/91 discloses a condenser for use in ear coolers which comprises a pair of headers arranged at right and left in parallel and spaced apart from each other, parallel flat refrigerant tubes each joined at its opposite ends to the two headers, corrugated fins arranged in an air flow clearance between adjacent refrigerant tubes and brazed to the adjacent refrigerant tubes, an inlet pipe connected to the upper end of the left header, an outlet pipe connected to the lower end of the right header, a left partition provided inside the left header and positioned above the midportion thereof, and a right partition provided inside the right header and positioned below the midportion thereof, the number of refrigerant tubes between the inlet pipe and the left partition, the number of refrigerant tubes between the left partition and the right partition and the number of refrigerant tubes between the right partition and the outlet pipe decreasing from above downward. A refrigerant flowing into the inlet pipe in a vapor phase flows zigzag through the condenser before flowing out from the outlet pipe in a liquid phase. Condensers of the construction described are called parallel flow or multiflow condensers, realize higher efficiencies, lower pressure losses and supercompactness and are in wide use recently in place of conventional serpentine condensers.
It is required that the flat refrigerant tube for use in the condenser have pressure resistance since the refrigerant is introduced thereinto in the form of a gas of high pressure. To meet this requirement and to achieve a high heat exchange efficiency, the refrigerant tube is made of a hollow aluminum extrudate which comprises flat upper and lower walls, and a reinforcing wall connected between the upper and lower walls and extending longitudinally. To improve the heat exchange efficiency and to compact the condenser, it is desired that the flat refrigerant tube have a small wall thickness and the lowest possible height. In the case of extrudates, however, the extrusion technique improses limitations on the reduction in the height of the tube and in the wall thickness.
The reinforcing wall in the refrigerant tube forms independent parallel refrigerant passages in the interior of the tube. Air flows orthogonal to the parallel refrigerant passages, so that the heat exchange efficiency is consequently higher at the air inlet side than at the air outlet side. Accordingly, gaseous refrigerant is rapidly condensed to a liquid in the refrigerant passage at the upstream side, whereas the refrigerant still remains gaseous in the refrigerant passage at the downstream side. When the entire structure of refrigerant tube is considered, the refrigerant therefore flows unevenly, failing to achieve a hugh heat exchange efficiency.
To overcome this problem, Unexamined Japanese Patent Publication No. 98896/89 discloses a flat refrigerant tube provided by an electric resistance welded tube. The disclosed refrigerant tube is internally divided into a plurality of refrigerant passages and has louvered wavelike inner fins inserted in and blazed to the tube for causing the refrigerant to flow between adjacent passages. Unexamined Japanese Patent Publication No. 136093/82 discloses an electric resistance welded flat refrigerant tube which is formed on its upper and lower walls with inwardly projecting reinforcing portions butting against each other end-to-end and shaped to a folded-in-two form, the reinforcing portions being arranged discretely in parallel longitudinally of the tube.
However, the former flat refrigerant tube is low in productivity since the wavelike inner fins need to be individually inserted into the tube. With the latter flat refrigerant tube in which the inwardly projecting reinforcing portions are formed by press work or rolling, the reinforcing portions have a V-shaped open cross section and are therefore insufficient in strength. Although the inwardly projecting reinforcing portions may be formed by rolling, this method inevitably leaves streaklike grooves in the upper and lower walls of the tube, so that when the tube is joined to the headers in communication therewith by brazing, the brazing agent is likely to flow out along the groove from the joint portion to be formed to produce a defective joint. Further provision of discrete reinforcing portions in the folded form on a flat sheet is likely to involve variations in dimensions to form refrigerant passages which are not uniform in size. Additionally since the material sheet remains unchanged in thickness when roll forming is resorted to, it is disadvantageous from the viewpont of the material to form the reinforcing portions by folding in two, while difficulty is encountered in forming many refrigerant passages of reduced width.
The main object of the present invention is to provide a refrigerant tube for use in heat exchangers which achieves a high heat exchange efficiency, is sufficient in pressure resistance and can be produced efficiently.